Communication was not as prevalent. The Middle East area was basically all that was known for the first few thousand years of human existence. It didn't go global until humans went global.

What I find the most interesting...if you go by Adam And Eve, they started all human life. They would have taught their children about God and so on...why all of a sudden did religion break off and create a variety of different cultures and religions just by the time of Noah? And then the world was destroyed, having only Noah and his family to restart everything and they would have taught their children about the one true God...and yet somewhere the populations exploded, people started worshiping Gods that they would have HAD to create out of thin air and new cultures were started.